This study will investigate the determinants of transitions into ill- health and one of the important proximate determinants--medical care utilizations. The project will illuminate both the evolution of health status and health service use that accompanies aging. We will examine adults of all ages in order to identify the age at which individuals make the transition from self-sufficiency to dependency. We will also investigate how the age of transition and medical care utilization are altered by individual socio-economic circumstances. Understanding the process of transition and its implications for medical care utilization are important elements in planning for aging. The proposed research will use data with several distinguishing features: (1) a larger number of health indicators that together measure overall health status, physical functioning, nutrition, acute morbidity, and elements of mental health such as depression and sleeplessness, (2) the health measures are available from two points in time, allowing us to analyze health transitions, (3) the health data is combined with detailed individual and household socio-economic data including information on health insurance and the family's social support network, (4) detailed data on health care utilization is available for two points in time allowing us to control for unobserved heterogeneity.